Production of crimped filaments



3&34393 PRODUCTION OF (IREWPED FILAMENTS John Burt Dawson, Aughton, Grmskirk, and Boieslaw Krzesinski, Chcylesmcre, Coventry, England, assignors to Courtaulds Limited, London, England, a British company No Drawing. Filed Aug. 31, 1962, Ser. No. 220,903 Claims priority, application Great Britain Sept. 4, 1961 7 Claims. ((Il. 18-54) This invention is concerned with the production of crimped filaments, in particular with a wet spinning process whereby crimped polyacrylonitrile filaments may be produced. By polyacrylonitrile we mean both homo polymers of acrylonitrile and also copolymers containing at least 80 percent by weight of acrylonitrile units. Such copolymers may be the products of copolymerisation with acrylonitrile of such other monomers as styrene, methyl acrylate, itaconic acid, methallyl .sulphonic acid and its salts, vinyl acetate and vinyl pyridine. The invention is particularly applicable to copolymers con taining 90 to 95 percent by Weight of acrylonitrile units.

It has already been proposed to produce crimped polyacrylonitrile filaments by a Wet spinning process, without the necessity of a mechanical crimping operation, by first spinning filaments having two chemically different zones across their width and then bringing about different shrinkage of the zones. The chemically difierent zones may consist of two copolymers of the same monomore in different proportions or of two different polymers, of which if desired only one may be an acrylonitrile polymer.

In both these cases it is necessary first to prepare two distinct polymers before the spinning can be carried out. It is an object of this invention to provide a process for wet spinning crimped polyacrylonitrile filaments wtihout mechanical crimping and using a single acrylonitrile polymer.

The process according to this invention comprises spinning simultaneously and adjacently into a liquid coagulant two solutions containing different concentrations of the same polyacrylonitrile polymer, the difference in concentrations being at least 4 percent of the smaller concentration and the two solutions being allowed to come into contact with each other before the polymer therein is wholly coagulated, stretching the resulting filaments to at least four times their unstretched length and drying the filaments under conditions allowing them to shrink.

The two solutions may be spun into the coagulant through closely adjacent jet holes but it is more satisfactory to spin the solutions simultaneously through the same jet hole. This latter method is best carried out by using a divided jet hole or by bringing the solutions into contact with each other only immediately behind the jet hole. Apparatus for carrying out these methods, ie, for spinning composite filaments, is already known in the filament-spinning art and need not be described here.

The dilference in concentration of the two solutions must be at least 4 percent of the smaller concentration. However, for more marked crimp effects it is preferred to use solutions having at least a 10 percent concentration difference, i.e. in which one concentration is at least 110 percent of the other. Since at high differences of concentration it may be necessary to employ solutions having unduly high or low concentrations, and at lower concentration differences the crimp effect is reduced, an optimum difiference lies at about 25 percent of the smaller concentration.

The two solutions of different concentrations may be amines Patented Apr. 9, 1963 solutions in the same or in different solvents. When different solvents are employed, however, the difiiculty of choosing a common coagulant arises and moreover, when the process is applied to a cyclic system in which the spent solvent is regenerated to be used again, there is the further problem of having to separate two solvents from the coagulant and from each other. Thus, whilst it is possible, for example, to spin solutions of different polyacrylonitrile concentration in dimethyl formamide and dimethyl sulphoxide into Water as the common coagulant, it is greatly preferred to employ two solutions of dilferent concentration in a comrnon solvent. The preferred solvent is an aqueous solution of an inorganic thiocyanate.

The stretch next applied to the two-component filaments so obtained is at least a four-fold stretch. Preferably the stretch is not greater than to 18 times the unstretched length, with an optimum value lying at about an eightor ten-fold stretch.

After stretching, the filaments are dried under conditions allowing them to shrink. These conditions may be achieved, for example, by drying the filaments in batches in an oven, either in hanks or wound loosely as a filament cake, or in a continuous system by drying them in festoons or supported on a moving conveyor. If they are dried continuously, the rate of feed of the filaments to the drying zone should exceed their rate of withdrawal from that zone, in order to allow the shrinkage and crimping of the filaments to take place. Preferably any tension applied to the filaments during the drying does not exceed 5 milligrams/ denier.

The drying may be carried out at a wide range of temperatures, varying from room temperature at the lower end of the range up to about 100 C. at the top. The lower temperatures are the most effective for obtaining high crimp ratios (by which we mean the ratio of the length of a selected piece of crimped filament with the crimp straightened out to the relaxed length of the filament). However, in order to carry out the drying in a short enough time for .the process to be carried out in a continuous manner, higher temperatures are desirable. A reasonable compromise of efiicient drying and good crimping may be obtained in the range of 60 to C.

When the present invention is carried out using two solutions of polymer in the same solvent, an important advantage of the invention may be realized by first preparing a single solution of the polymer and, while feeding that solution to the spinning jet, separating a portion of the solution, diluting it with additional solvent and feeding the diluted solution separately to the jet as the second polymer solution. In this way, not only is the necessity for preparing two polymers avoided (as applies in all forms of the present invention), but also only one polymer solution need be prepared. In addition, the crimp may be controlled, if desired, by controlling the diluting of that solution. Furthermore, since the two components of the crimped fibre are of the same chemical composition, it is much easier to obtain uniform dyeing than is the case using previously known forms of bi-component filaments.

The invention will now be further described by means of the following examples, in each case the polymer used being a copolymer containing acrylonitrile and methyl acrylate units in the proportion of 94:6 and the solvent being a 51 percent solution by weight of sodium thiocyanate in Water. The solution-s of different concentration were spun through a jet having 188 holes, each of 4 mil-s diameter, the two liquid streams to each jet hole being allowed to mingle at a distance behind the hole which was varied between the examples from 4 mils to 105 mils. The coagulant bath was an 11 percent by weight solution of sodium thiocyanate in water. The stretch was varied between the examples by varying the peripheral speed of the take-up roller (i.e. the first roller from the jet) and keeping the final linear filament speed constant at 20 metres/minute. The denier of the resulting filaments was about 3.5.

Example 1 Example 2 Using two solutions containing 12.4 and 9.1 percent by weight respectively of the polymer and varying the degree of stretch applied before drying the filaments at 80 C., the following results were obtained:

Stretch (times) Crimp Ratio Orimps/inch Example 3 The two concentrations by weight of polymer were 6.4 and 12.4 percent respectively. After stretching eight-fold and drying at 80 C., the filaments had a crimp ratio of about 1.3 and had 35 crimps/inch.

Example 4 Two solutions of polymer having concentrations by weight of 11.9 and 12.4 percent respectively were spun to form a composite filament, stretched eight-fold and dried. When drying was carried out at 80 C., the crimp ratio of the filaments obtained was about 1.1 and the filaments had 5 crimps/inch. When drying was carried out at room temperature, the crimp ratio was 1.2 and the number of crimps was ll/inch.

What we claim is:

1. A process for producing crimped polyacrylonitrile filaments, comprising spinning simultaneously and adjacently into a liquid coagulant two solutions containing different concentrations of the same polyacrylonitrile polymer, the difference in concentrations being at least 4 percent of the smaller concentration and the two solutions being allowed to come into contact with each other before the polymer therein is wholly coagulated, stretching the resulting filaments to at least four times their unstretched length and drying the filaments under conditions allowing them to shrink.

2. A process for producing crimped polyacrylontirile filaments, comprising forming filaments, each of which has at least two components eccentrically disposed with respect to each other, from two solutions of the same polyacrylonitrile polymer, one of which solutions has a concentration of polymer equal to at least 104 percent of the concentration of polymer in the other solution, subjecting the filaments to an at least four-times stretch and thereafter drying the stretched filaments while allowing them to shrink.

3. A process for producing crimped polyacrylonitrile filaments, comprising forming two solutions of the same polymer in the same solvent, the solutions having a difference in concentration of polymer equal to at least 4 percent of the smaller concentration, spinning the solutions to form filaments each having two components in side-by-side relationship, stretching the filaments by at least a four-fold amount and drying the filaments while allowing them to shrink.

4. -A process as claimed in claim 3, in which the difierence in concentration is at least 10 percent of the smaller concentration.

5. A process for producing crimped polyacrylonitrile filaments, comprising continuously supplying a solution of polyacrylonitrile to a filament-spinning system, continuously separating a portion of said solution from said supply, continuously diluting said separated portion to give a second solution such that the concentration of the first-mentioned solution is at least 104 percent of that of the second solution, spinning the two solutions to form two-component filaments having the two components disposed side-by-side, stretching the filaments to between four and eighteen times their unstretched length and then drying the filaments while allowing them to shrink.

6. A process as claimed in claim 5, in which the sol vent is a solution of sodium thiocyanate.

7. A process as claimed in claim 6, in which the filaments are dried at a temperature in the range of to C.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS FOR PRODUCING CRIMPED POLYACRYLONITRILE FILAMENTS, COMPRISING SPINNING SIMULTANEOUSLY AND ADJACENTLY INTO A LIQUID COAGULANT TWO SOLUTIONS CONTAINING DIFFERENT CONCENTRATIONS OF THE SAME POLYACRYLONITRILE POLYMER, THE DIFFERENCE IN CONCENTRATIONS BEING AT LEAST 4 PERCENT OF THE SMALLER CONCENTRATIONS AND THE TWO SOLUTIONS BEING ALLOWED TO COME INTO CONTACT WITH EACH OTHER BEFORE THE POLYMER THEREIN IS WHOLLY COAGULATED, STRETCHING THE RESULTING FILAMENTS TO AT LEAST FOUR TIMES THEIR UNSTRETCHED LENGTH AND DRYING THE FILAMENTS UNDER CONDITIONS ALLOWING THEM TO SHRINK. 